1. Field of the Invention
The present invention relates to a display device and an operating method of the display device. In particular, the present invention relates to a method for improving quality of a moving image of a hold-type display device.
2. Description of the Related Art
In recent years, there have been growing interests in thin display devices. Liquid crystal displays, plasma displays, projection displays, and the like have been developed and becoming popular instead of CRT displays. Further, field emission displays, inorganic electroluminescence displays, organic electroluminescence displays, electronic paper, and the like have been developed as next-generation display devices.
In a display portion which is provided in the above-described display device, pixels which are minimum units for forming an image are arranged. Each of the pixels emits light with desired luminance by being supplied with a signal generated by image data. Accordingly, an image is displayed in the display portion.
In addition, the signal supplied to the pixel is updated (refreshed) at a constant period. An inverse number of this period is referred to as a frame rate. Further, time after the signal is updated once and before the signal is updated next is referred to as one frame period. Display of a moving image in the display portion is realized by supplying a signal which is different from the signal supplied before to the pixel when the signal is updated. On the other hand, display of a still image in the display portion is realized by supplying a signal which is the same as the signal supplied before to the pixel when the signal is updated.
Further, driving methods of display devices can be classified by temporal distribution of luminance of a pixel in one frame period. In hold-type display devices which are used for active matrix display devices, a pixel continuously emits light in one frame period. On the other hand, in impulsive-type display devices typified by CRTs, a pixel immediately attenuates and does not emit light after the pixel strongly emits light once in one frame period. In impulsive-type display devices, most one frame period is a non-light emitting state.
It has become obvious that hold-type display devices have a problem such that a moving object seems to leave traces when a moving image is displayed and part of an image is moved or the entire image blurs when the entire image is moved (motion blur). This is characteristics of hold-type display devices and a problem of motion blur does not occur in impulsive-type display devices.
As a method for solving a problem of motion blur in hold-type display devices, the following two methods have been mainly proposed (see Reference 1). A first method is a method of providing a period during which the original image is displayed and a period during which a black image is displayed in one frame period. Thus, display can be made closer to that of impulsive-type display devices, so that quality of a moving image can be improved (see References 2 and 3). A second method is a method in which display is performed by shortening the length of one frame period (increasing a frame rate) and generating a temporally compensated image with respect to an increased frame at the same time. Thus, quality of a moving image can be improved (see Reference 4). In addition, as an improvement technology of the first method, it is disclosed that quality of a moving image can be improved by displaying a darker image than the original image instead of a black image (see References 5, 6, 9, 10, and 11). Further, a method of changing driving methods in accordance with conditions is also disclosed (see Reference 7 and 8).    [Reference 1] Japanese Published Patent Application No. H04-302289    [Reference 2] Japanese Published Patent Application No. H09-325715    [Reference 3] Japanese Published Patent Application No. 2000-200063    [Reference 4] Japanese Published Patent Application No. 2005-268912    [Reference 5] Japanese Published Patent Application No. 2002-23707    [Reference 6] Japanese Published Patent Application No. 2004-240317    [Reference 7] Japanese Published Patent Application No. 2002-91400    [Reference 8] Japanese Published Patent Application No. 2004-177575    [Reference 9] Society For Information Display '05 DIGEST, 60.2, pp. 1734 to 1737, (2005)    [Reference 10] Society For Information Display '06 DIGEST, 69.4, pp. 1950 to 1953, (2006)    [Reference 11] Society For Information Display '06 DIGEST, 69.5, pp. 1954 to 1957, (2006)